MODELING THE F-LAYER DURING SPECIFIC GEOMAGNETIC STORMS

Important progress has been made recently in developing an understandi ng of the effects of geomagnetic storms in the thermosphere and ionosp here. Numerical simulations of theoretical storms with the coupled the rmosphere ionosphere model (CTIM) have provided a better understanding of the dynamics of the upper atmosphere and have also permitted the i dentification of the processes responsible for global storm effects at highlatitude and midlatitude. The theory developed based on the model simulations can explain most of the apparent coherence of local time and seasonal dependencies and the apparent randomness in the longitudi nal response of the global ionosphere, uncovered through statistical a nalysis of storm observations. A true test of the model and the theory is their ability to predict the large-scale distribution of storm eff ects for specific storms. In this paper, CTIM simulation results for t he December 79, 1982, period are presented. We compare model results w ith DE 2 temperature and plasma density data. We also compare modeled electron densities with ionosonde data from several sectors in both he mispheres. The global characteristics of the response are reproduced b y the model, and we are able to explain the pronounced longitude diffe rences in the summer hemisphere. The Australian sector passes through midnight during the main driven phase of the storm and experiences the largest energy input and the largest neutral composition changes. The deepest ionospheric negative phase seen in ionosonde data is over Aus tralia and is consistent with this interpretation. Given the large unc ertainties in our knowledge of the magnitude and spatial distribution of energy input during a particular storm, predicting local changes is still a challenge.